1. Field of the Invention
The invention relates to an apparatus for polishing an object in the form of a plate, such as a semiconductor wafer, a wafer covered with an insulating film in a semiconductor circuit, a wafer on which a metal wire is formed, a magnetic disc or a glass substrate. The invention relates further to a method of doing the same.
2. Description of the Related Art
There have been suggested many apparatuses and methods for polishing an object in the form of a plate, such as a semiconductor wafer, a magnetic disc or a glass substrate.
For instance, Japanese Unexamined Patent Publication No. 5-69310 has suggested an apparatus for polishing an object, including a flexible resilient film on which a wafer lies.
Japanese Unexamined Patent Publication No. 5-309559 has suggested an apparatus and a method of polishing an object, in which a laser beam is radiated to an object, a reflected laser beam is received, and then, a thickness of the object is measured based on the reflected laser beam.
Japanese Unexamined Patent Publication No. 7-105369 has suggested a method including the steps of a coating an organic resist containing a specific molecule, pigment or chemical compound therein, onto a substrate, analyzing used polishing solution, detecting the molecule, pigment and chemical compound, controlling a rotation speed, a load pressure, and a location of an apparatus of polishing an object based on the results of detection.
Japanese Unexamined Patent Publication No. 9-11117 has suggested an apparatus including a dresser for dressing a polishing cloth with which an object is to be polished. The dresser is positioned in a direction of a radius of a polishing plate supporting the polishing cloth therewith.
Japanese Unexamined Patent Publication No. 11-179648 has suggested an apparatus of polishing an object, including a conditioner, and absorbers positioned around the conditioner. Dust generated as the result of conditioning a polishing pad is collected by the absorbers.
Japanese Unexamined Patent Publication No. 11-48122 has suggested an apparatus of polishing an object, including a first dresser and a second dresser. The first dresser grinds and hence planarizes a surface of a polishing pad. Thereafter, the polishing pad is dressed by the second dresser comprised of a cylindrical brush, to thereby recover an original rough grain.
FIG. 1 is a side view of a conventional apparatus of polishing an object, similar to the apparatuses suggested in the above-mentioned Publications.
In operation of the apparatus, an object 132 is kept lied on a surface of a circular polishing plate 131 under a pressure by means of a holder 133. While the polishing plate 131 is being rotated, polishing solution 134 containing abrasive is supplied to a surface of the polishing plate 131 to thereby polish the object 132.
FIG. 2 is a graph showing a relation between a polishing rate and a period of time in which the object 132 is polished, in the apparatus illustrated in FIG. 1. Herein, the polishing rate is defined as A/B wherein A indicates a polished amount of the object and B indicates a polishing time. As is obvious in view of FIG. 2, as the polishing time becomes longer, the polishing rate becomes smaller, because a surface of the polishing plate 131 is covered with particles generated by polishing the object 132. Thus, the conventional apparatus illustrated in FIG. 1 is accompanied with a problem that objects are polished in different degrees.
In addition, since polishing solution used for polishing the object 132 is wasted each time the object 132 is polished, the conventional apparatus is accompanied with another problem that running costs are unavoidably high.
Hence, the inventor of the present invention has suggested an apparatus for polishing an object, in Japanese Unexamined Patent Publication No. 11-70459, including a rotatable circular polishing plate having a polishing surface on which an object is to be polished, a pressurizer which applies a pressure to an object to make the object contact with the polishing surface, a first unit which is located upstream of the object in a direction of rotation of the polishing plate and which supplies polishing solution containing abrasive, to the polishing surface, a dresser which is located downstream of the object in a direction of rotation of the polishing plate and which dresses the polishing surface, and a second unit which is located downstream of the dresser and upstream of the first unit in a direction of rotation of the polishing plate and which has an absorption surface through which the second unit sucks the polishing solution from the polishing surface.
In practical use, the apparatus works better than the conventional apparatus illustrated in FIG. 1. However, the apparatus has the following problems.
Firstly, it is necessary to keep a gap between the absorption surface and the polishing surface to be equal to or smaller than 1 mm in order to ensure a sufficient ability of the second unit to absorb the polishing solution. However, if the polishing plate is worn and hence the gap becomes greater, an ability of the second unit to absorb the polishing solution is reduced.
Secondly, each time the polishing plate is exchanged to a new one, it takes much time to properly set the second unit, resulting in deterioration in productivity.
In view of the above-mentioned problems in the conventional apparatuses, it is an object of the present invention to provide an apparatus and a method of polishing an object, both of which can keep a sufficient ability of the second unit to absorb polishing solution, even if the polishing plate is worn, and which makes it easier to properly set the second unit.
In one aspect of the present invention, there is provided an apparatus for polishing an object, including (a) a rotatable circular polishing plate having a polishing surface on which an object is to be polished, (b) a pressurizer which applies a pressure to an object to make the object contact with the polishing surface, (c) a first unit which is located upstream of the object in a direction of rotation of the polishing plate and which supplies polishing solution containing abrasive, to the polishing surface, (d) a dresser which is located downstream of the object in a direction of rotation of the polishing plate and which dresses the polishing surface, and (e) a second unit which is located downstream of the dresser and upstream of the first unit in a direction of rotation of the polishing plate and which has an absorption surface through which the second unit sucks the polishing solution from the polishing surface, the absorption surface being formed thereon with a plurality of pivots.
In accordance with the apparatus, since the absorption surface of the second unit is designed to have a plurality of pivots, it would be necessary to keep a gap between the absorption surface and the polishing surface equal to a height of the pivots. Thus, the second unit could be readily set each time the polishing plate is exchanged to a new one.
It is preferable that each of the pivots has a rounded summit. This ensures smooth contact between the pivots and the polishing surface of the polishing plate.
Though the pivots may be formed anywhere on the absorption surface, it is preferable that the pivots are formed at four corners of the absorption surface.
This ensures a widest area of the absorption surface.
The pivots may be composed of any material. For instance, the pivots may be composed of Teflon.
The absorption surface may be comprised of a first area facing an inner area of the polishing surface, a second area facing an outer area of the polishing surface entirely surrounding the inner area, and an intermediate area located between the first and second areas, the first area having absorption holes in a greater number than the intermediate area and the second area having absorption holes in a greater number than the intermediate area. The polishing solution is absorbed into the second unit through the absorption holes.
The rotating polishing plate exerts a centrifugal force on the polishing solution, and accordingly, the polishing solution tends to flow radially outwardly of the polishing plate. Hence, by forming the absorption holes in the first and second areas in a greater number than the intermediate area, it would be possible to effectively absorb the polishing solution, in particular, in an outer area of the polishing surface facing the second area.
It is preferable that the absorption surface is formed at opposite edges thereof with a plurality of recesses in a direction of rotation of the polishing plate.
Such recesses could catch the polishing solution flowing towards a periphery of the polishing plate by a centrifugal force exerted by the rotating polishing plate.
It is preferable that the absorption surface is rounded or chamfered at opposite edges thereof in a direction of rotation of the polishing plate.
This ensures that, even if the second unit makes direct contact with the polishing surface of the polishing plate, it would be possible to prevent both the second unit and the polishing plate from being damaged.
The apparatus may further include a unit for rotating the dresser around a center of the dresser.
The unit makes is possible to vary a relative speed between the polishing surface of the polishing plate and a dressing surface of the dresser, and to rotate the dresser in a direction opposite to a direction in which the polishing plate rotates, thereby adjusting a degree of dressing the polishing surface.
The apparatus may further include a unit for upwardly or downwardly moving the second unit relative to the polishing surface.
The unit ensures that a gap between the absorption surface and the polishing surface is kept constant, even if a polishing pad equipped in the polishing plate is worn. The unit may be comprised of a screw or a combination of a motor and a screw automatically rotated by the motor.
The apparatus may further include an annular wall standing along a periphery of the polishing plate and rotatable together with the polishing plate, and a third unit which is located inside the annular wall and in the vicinity of an inner surface of the annular wall and which collects the polishing solution.
The annular wall facilitates collection of the polishing solution and capture of debris generated by polishing an object, and the third unit surely removes the polishing solution having been not absorbed by the second unit.
It is preferable that the second unit and the dresser are integrally supported on the polishing surface so that the second unit and the dresser are rotatable together in a direction of rotation of the polishing plate.
Since the second unit and the dresser are rotatable on the polishing surface, it would be possible to uniformly dress the polishing surface and uniformly absorb the polishing solution, as the polishing plate rotates.
It is preferable that the apparatus further includes a fourth unit which reciprocates the second unit and the dresser together in a direction of a radius of the polishing plate.
As an alternative, the second unit may have a length equal to a radius of the polishing surface, and the second unit lies above the polishing plate entirely over a radius of the polishing surface.
As an alternative, the dresser may have a length equal to a radius of the polishing surface, and the dresser lies on the polishing plate entirely over a radius of the polishing surface.
The fourth unit, the second unit having such a length or the dresser having such a length would make it possible to absorb the polishing solution over an entire radius of the polishing surface, ensuring that any object can be polished under the same conditions regardless of a size of the object.
It is preferable that the apparatus further includes a fifth unit which filters the polishing solution having been absorbed by the second unit, and supplies the thus filtered polishing solution to the first unit.
The fifth unit makes it possible to recycle the polishing solution, and hence, ensures reduction in running costs of the apparatus.
There is further provided an apparatus for polishing an object, including (a) a rotatable circular polishing plate, (b) a pressurizer which applies a pressure to an object to make the object contact with the polishing surface, (c) a first unit which is located upstream of the object in a direction of rotation of the polishing plate and which supplies polishing solution containing abrasive, to the polishing surface, and (d) a dresser which is located downstream of the object in a direction of rotation of the polishing plate and which dresses the polishing surface, the dresser including a second unit having an absorption surface through which the second unit sucks the polishing solution from the polishing surface, the absorption surface being formed thereon with a plurality of pivots.
In accordance with the apparatus, it would be possible to firstly dress the polishing surface of the polishing plate by the dresser, and secondly, absorb the polishing solution by the second unit integrally formed with the dresser.
For instance, the dresser may be in the form of a circle.
The dresser may be formed of a circular plate in which a dressing surface of the dresser and the absorption surface are radially and alternately arranged.
Since the dressing surface and the absorption surface are radially alternately arranged, dressing the polishing surface and absorbing the polishing solution and debris are repeatedly cyclically carried out.
The dresser may be formed of a circular plate in which the absorption surface is arranged in an inner area of the circular plate and a dressing surface of the dresser is arranged in an outer area surrounding the inner area of the circular plate.
Since the absorption surface and the dressing surface are arranged adjacent to each other, dressing the polishing surface and absorbing the polishing solution and debris are concurrently carried out.
The dresser may be formed of a circular plate in which a dressing surface of the dresser and the absorption surface are coaxially and alternately arranged.
Since the absorption surface and the dressing surface are coaxially arranged, dressing the polishing surface and absorbing the polishing solution and debris are repeatedly cyclically carried out.
The dresser may be formed of a cylinder, a dressing surface of the dresser extending in an axial direction of the cylinder and the absorption surface extending in an axial direction of the cylinder being alternately arranged on an outer surface of the cylinder.
Since the dressing surface and the absorption surface are alternately arranged in an outer surface of the cylinder, when the cylinder rotates, dressing the polishing surface and absorbing the polishing solution and debris are repeatedly cyclically carried out.
The dresser may be formed of a circular plate in which a plurality of the dressers are arranged on a certain circumference and an area other than the dressers is formed as absorption surface.
By using the dresser, dressing the polishing surface and absorbing the polishing solution and debris are concurrently carried out.
It is preferable that a dressing surface of the dresser projects beyond the absorption surface, preferably, by 1 mm or smaller.
By designing the dressing surface to project beyond the absorption surface, it would be possible to properly dress the polishing surface and absorb the polishing solution.
In another aspect of the present invention, there is provided a method of polishing an object, comprising the steps of (a) causing an object to make a contact with a polishing surface of a rotating polishing plate under pressure, and supplying polishing solution containing abrasive, to the polishing surface at a first location upstream of the object in a direction of rotation of the polishing plate, (b) digging the polishing solution from the polishing surface at a second location downstream of the object in a direction of rotation of the polishing plate, and (c) sucking the polishing solution from the polishing surface at a location downstream of the second location and upstream of the first location in a direction of rotation of the polishing plate.
In accordance with the method, the polishing solution is dug from the polishing surface by the dresser at a location downstream of the object, and the thus dug polishing solution is absorbed by the second unit, while the object is being polished. Hence, the polishing solution and debris of both the object and the polishing plate are removed in an in-process manner, ensuring that the polishing surface are kept clean.
The steps (b) and (c) may be concurrently carried out.
The method may further include the steps of filtering the polishing solution having been sucked in the step (c), and supplying the thus filtered polishing solution to the polishing surface.
This ensures that the polishing solution is filtered, and then, the thus filtered polishing solution is supplied again to the polishing surface. Hence, the polishing solution can be repeatedly used, ensuring reduction in running costs. In addition, it would be possible to reduce an environmental load to be caused by wasting the polishing solution.